EFFECTS OF ADMINISTRATION OF HUMAN CHORIONIC GONADOTROPIN OR PROGESTERONE BEFORE MATERNAL RECOGNITION OF PREGNANCY ON BLASTOCYST DEVELOPMENT AND PREGNANCY IN SHEEP

A series of four experiments with 258 ewes was conducted to determine whether blastocyst size could be altered before normal luteolysis and, if so, how this affected fertility. In Exp. 1 and 2, nonmated and mat ed ewes, respectively, were treated with hCG (100 IU), progesterone (1 2 mg), or vehicle on d 11.5 (d 0 = onset of estrus). In Exp. 3 and 4, field trials were conducted to compare the effects of either hCG or pr ogesterone treatment on d 11.5 on subsequent pregnancy rates. In Exp. 1, hCG transiently increased (P <.01) concentrations of progesterone a nd estradiol in plasma, whereas progesterone treatment increased only plasma progesterone. Neither hCG nor progesterone affected the duratio n of the estrous cycle. In Exp. 2, d-13 blastocysts were longer (3.5 /- 1.6 vs.8 +/- .5 cm; Mean +/- SE; P <.05), and concentrations of pro tein and interferon tau (IFN tau) in uterine flushings were greater (1 0.7 vs 1.2 mu g; P < .05) in hCG- than in vehicle-treated ewes. Proges terone treatment did not affect blastocyst development. In Exp. 3, pre gnancy rates tended to be greater (P < .10) in ewes given hCG than in those given vehicle (44/47; 94% vs 40/48; 83%); however, administratio n of progesterone in Exp. 4 had no effect on pregnancy rates (P <.14; 41/45; 91% vs 37/46; 80%; control ewes). These results indicate that t reatment with hCG on d 11.5 stimulated uterine secretions and conceptu s growth sufficiently to influence pregnancy rates.